An ice exclusion zone has been introduced to the Volvo Ocean Race after a 300-metre-long iceberg was spotted by organisers.

The fleet of seven teams is nearing the end of the first leg from Alicante, Spain, to Cape Town, South Africa.

"Icebergs are the one thing that sailors are most afraid of," said Mark Covell, part of the race control team.

Abu Dhabi Ocean Race, skippered by Briton Ian Walker, was leading by just 17 nautical miles on Saturday.

All of the fleet are sailing in a one-design Volvo Ocean 65 boat, built for durability rather than speed. The opening stage has been the most closely contested in the event's history, with the early leaders and all-female Team SCA currently in last place.

Justin Slattery, part of the Abu Dhabi crew, said: "It doesn't take much to sink a boat like this."